Pyomyositis is a purulent infection of skeletal muscle that arises from hematogenous spread, usually with abscess formation [1]. The clinical approach to pyomyositis will be reviewed here. Other soft tissue infections such as clostridial myonecrosis and necrotizing fasciitis are discussed separately. (See "Clostridial myonecrosis" and "Necrotizing soft tissue infections".)

EPIDEMIOLOGY

Pyomyositis is classically an infection of the tropics, although it has been recognized in temperate climates with increasing frequency [2-8]. Tropical pyomyositis primarily occurs in two age groups: children (ages 2 to 5) and adults (ages 20 to 45), while the majority of temperate pyomyositis cases occurs in adults. Males appear to be more commonly affected than females. Most patients with tropical pyomyositis are otherwise healthy without underlying comorbidities, while most patients in temperate regions are immunocompromised or have other serious underlying conditions.

Immunodeficiency — Immunodeficiency has been implicated in the development of pyomyositis in both temperate and tropical climates. Forms of immunodeficiency associated with pyomyositis include HIV infection, diabetes mellitus, malignancy, cirrhosis, renal insufficiency, organ transplantation, and administration of immunosuppressive agents [2,14].

HIV is a particularly important risk factor [2,4,7,12,15-19]. A case-control series in Uganda demonstrated a significant association between pyomyositis and HIV infection [7]. In a review of 98 cases in North America, about half of pyomyositis patients with underlying medical conditions were seropositive for HIV [4]. The mechanism of HIV infection in the predisposition to pyomyositis is unclear; factors may include immune compromise, primary HIV myopathy, antiretroviral therapy, and increased rates of staphylococcal carriage [2,7,18,19].

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